This proposal will use psychophysical and psychophysiological procedures to study binocular rivalry, the breakdown in stable binocular single vision resulting from discordant monocular inputs. During rivalry the eyes convey contradictory information to the brain about the nature of objects at given locations in visual space. Faced with rival interpretations, the brain lapses into an unstable state characterized by alternating periods of monocular dominance that continue as long as the eyes view discordant stimuli. The study of rivalry has bearing on several key issues in vision science including the possible neural bases of strabismic suppression, the principles of perceptual organization, neural mechanisms involved in fusion and stereopsis, and possible neural concomitants of conscious visual awareness. Interest in rivalry has grown in recent years, but several important issues remain unresolved, issues that bear importantly on the nature and locus of binocular rivalry. The proposed work will study several of these: a) what actually rivals during rivalry, competing stimulus interpretations or conflicting image features associated with left and right eyes, b) the role of global context in determining the temporal dynamics of rivalry, c) the extent to which a stimulus suppressed from vision can still contribute to perceptual grouping and scene interpretation, and d) whether rivalry is affected when dissimilar monocular stimulation is consistent with ecologically valid stimulus conditions. Using several different techniques (test probe procedure, startle reflex, tracking procedure, forced-choice testing), the proposed experiments are intended to resolve outstanding controversies concerning rivalry, including the "eye" vs. "stimulus" accounts of rivalry. In addition, results from these proposed experiments will provide guidance to neurophysiologists and cognitive neuro scientists seeking to discover the actual neural concomitants of rivalry.